1. Field of the Invention
The invention relates to a multi-source/receiver system in which the data source (sources) and data receiver (receivers) are connected to a communication bus which consists of at least one transfer medium which is suitable for the transport of at least one logic level (0 or 1).
2. Description of the Prior Art
Systems of this kind are known, notably systems in which the data sources and receivers consist at least partly of signal processor units such as microprocessors etc. Due to the increasing availability of micro-electronics in the form of increasingly further integrated electronic functions on so-called chips, the time has come for the application of micro-electronics in fields where costs have to be minimized; for example, in consumer products such as video equipment, audio equipment, etc. When co-operation between different apparatus in a network (for example, video or audio network of equipment) is desirable or required, communication between the various parts will be necessary. Given apparatus or parts thereof will then act as a data source or a data receiver or may even combine both functions. In a system comprising a number of data sources and receivers it is known to use a so-called communication bus for mutual communication; for example, see the article by Casaglia in Euromicro Newsletter, October 1976, Volume 2, No. 4, page 5 and further. Thus far, these communication buses had ample capacity, which means that they included a number of lines which provide smooth execution of the communication. Systems comprising 4-line and 8-line buses etc. are universally known. The most direct approach to the problem of an asynchronous communication between sources and receivers requires four lines: at least one data line and three handshake lines. According to this solution (for example, see Fall Joint Comp. Conf. 1972, pages 719-740) communication is possible between the modules without it being necessary for the modules to know each other's processing speed. However, a communication bus of this kind is too complex and often too expensive for use as a bus in fields where the costs have to be minimized.
Solutions have been pursued where the communication bus and hence the communication to be executed thereby is as simple and inexpensive as possible. Notably a bus comprising a minimum number of transfer lines would qualify in this respect. Minimum means at least one transfer medium which is suitable for the trasport of at least one logic level (0 or 1). In practice this may be a coaxial cable, a twisted core pair or also a wireless connection, or an optical fiber connection. In the latter examples, for example, there may be a connection by way of a carrier wave modulated with at least the logic level 0 or 1, or an infrared beam or light beam. A known example of a multi-source/receiver data processing system of the described kind is published in the conference papers known as EUROMICRO 1976: R. Sommer, "Cobus, a firmware controlled data transmission system", pages 299-303. "Cobus" stands for coaxial bus. Communication is realized thereby between a number of stations comprising microprocessors. However, this system does not satisfy the requirements as regards low cost. Also, the requirements as regards timing in the various processors are rather severe. For smooth execution of communication, the participating processors must know the bit periods of the other processors. This means that each processor must include an expensive crystal oscillator, or that the system must include a central clock, or that a timing network has to be trimmed after assembly, which is also expensive and notably unreliable.
Such an inexpensive and reliable solution also implies a simple solution, because once a system of this kind is in operation (for example, in a consumer home), special trimming and other adaptation steps may no longer be necessary. This is even more applicable when the addition of new data sources and/or data receivers at a later stage is a feature of the system.